As lithium-ion secondary batteries, there are known those that, use a liquid electrolyte as an electrolyte provided between electrodes (a positive electrode and a negative electrode) and, in addition, those that use a solid electrolyte. The lithium-ion secondary battery that uses a solid electrolyte has such advantages that it is possible to suppress liquid leakage and firing that may occur in a lithium-ion secondary battery using a liquid electrolyte and it is excellent in cycle characteristics. The lithium-ion secondary battery that uses solid materials for electrodes and an electrolyte is referred to as, for example, an all-solid lithium-ion secondary battery.
As materials usable for the solid electrolyte, that is, as a lithium-ion conductor, there are known materials, such as Li2S—P2S5-based, Li2S—P2S5—B2S3-based and Li3PO4—Li2S—B2S3-based materials, containing lithium (Li), phosphorus (P), boron (B), sulfur (S), oxygen (O) and the like. In addition, a germanium (Ge)-added material represented by a composition formula of Li4-xGe1-xPxS4, a material represented by a composition formula of Li7PS6-xSex (0≦x≦6), etc. are also known.
Japanese Laid-open Patent Publication No. 2003-22707
Japanese Laid-open Patent Publication No. 2003-68361
Japanese Laid-open Patent Publication No. 2009-193803
Chemistry—A European Journal, Vol. 16, pp. 5138 to 5147, 2010
Conventional lithium-ion conductors do not give sufficient ion conductive property and, when a conventional conductor is used as a solid electrolyte of an all-solid lithium-ion secondary battery, in some cases intended battery characteristics are not obtained.
Further, depending on the element contained in a lithium-ion conductor, the increase in cost and increase in weight of a solid electrolyte and an all-solid lithium-ion secondary battery containing the same may be brought about.